Assistance features for creating programs in apparatuses for creating NC machining programs have been enhanced in recent years, and NC machining programs have been able to be easily created by an operator's establishing coordinate values of an object to be machined, while viewing a production drawing. Further, an apparatus for creating an NC machining program has also appeared in the market such that an NC machining program can be created by directly loading into the apparatus, CAD data modeled by a designer using a CAD system.
However, a method has been used such that when the operator, while viewing the production drawing, performs direct programming of (modification of) the NC machining program, the operator calculates machining target dimensions by manual calculation or using a calculator and also enters in the NC machining program, coordinate values corrected based on the calculation results. A problem with this method has been that complicated modification of the NC machining program is likely to cause errors in calculation and/or data entry, resulting in the created NC machining program lacking reliability.
For this reason, a method has been proposed (refer to Patent Document 1) such that when a molded structure is machined into a final structure, machining margin (finish margin) data is entered on a screen for a machining surface needing a surface finish, to create data of a structure to which the machining margin has been provided; next, a tool path of a tool head with respect to the structure with the machining margin is created for interference checking on the screen; and in states where interference occurs, the operator changes the tool to a longer one, and rechecks the interference, whereby tool path data for machining the machining margin is created.
Further, an apparatus has been proposed as another example of the related art (refer to Patent Document 2) in which an attribute list is prepared where attributes, their corresponding machining margin amounts and the like are established in advance; the apparatus includes a final workpiece CAD that creates final workpiece shape data having attributes imparted to surfaces of a final workpiece, an interim workpiece CAD that creates, based on the final workpiece shape data and the attribute list, interim workpiece shape data in which machining margins that have the machining margin amounts corresponding to attributes of surfaces of a final workpiece shape have been provided to each of the surfaces, and an interim workpiece machining CAM that automatically calculates, based on the final workpiece shape data and the attribute list, a tool path for cutting the machining margins shape from the interim workpiece shape.